A so-called a gas-scavenged spark plug has at least one supply passage for an enrichment fuel that opens into its pre-chamber. Spark plugs of this type are frequently screwed into sleeves that are placed in a cylinder head of an internal combustion engine, in particular a stationary gas engine, and have coolant from the internal combustion engine flowing around them for the purpose of cooling, and hence are also referred to as “water sleeves.” The supply of fuel to the spark plug can take place through the water sleeve. At the same time, cooling of the spark plug takes place through the water sleeve.
Today, many internal combustion engines, especially large gas engines, are intended to operate by preference in lean-burn operation. A very lean fuel/air mixture is then present in the combustion chamber of the internal combustion engine, for which mixture the ratio—lambda—of the quantity of air that is actually present in the combustion chamber to the quantity of air stoichiometrically necessary for complete combustion of the fuel is greater than 1. Very lean fuel/air mixtures are difficult to ignite.
Described in DE 10 2013 210 125 A1 is a system composed of a water sleeve and a spark plug of the initially mentioned type with a pre-chamber delimited by a cap, in which enrichment fuel is delivered to the pre-chamber as additional fuel through supply passages provided in the spark plug, so as to be able to more easily ignite the fuel/air mixture present in the pre-chamber. The fuel/air mixture ignited in the pre-chamber then shoots through openings in the cap into the combustion chamber of the internal combustion engine and reliably ignites the much leaner mixture there.
DE 10 2013 210 125 A1 describes a spark plug having a body in which is provided a very narrow, multiple angle supply passage for an enrichment fuel. For all intents and purposes, a supply passage of this nature is not manufacturable with acceptable effort. To simplify manufacturability, DE 10 2013 210 125 A1 describes additional embodiments in which a sleeve is arranged between the insulator and the enclosing body. A necessary seal between the insulator and the body can be degraded by this sleeve located within the body. Furthermore, an annular gap extending in the circumferential direction of the spark plug is provided between the sleeve and the body; this gap impairs heat dissipation from the insulator nose and the center conductor projecting therefrom to the body.